Some present may remember an entertaining (not to mention illuminating (pun intended) ) blog by Professor Larry Moran:
I am a high school Biology teacher and Professor Moran threw out some challenges which cut me to the quick.
Here is a very brief and incomplete summary:
The dual photosystems of Blue-Green Algae clearly evolved late from a combination of a type I reaction center in species like Heliobacter and green sulfur bacteria and a type II reaction center from species like purple bacteria and green filamentous bacteria. The oxygen evolving complex was a late addition.
Both photosystems employ Porphyrins and Carotenoids which are important in various metabolic processes (not just photosynthesis) meaning their evolutionary history may reflect many other functions only to be co-opted later for photosynthesis. Meanwhile both can be demonstrated to have abiogenic origins.
Meanwhile RuBisCO is found in non-photosynthetic species…
According to Professor Moran, many misconceptions are perpetuated when teaching according to textbook orthodoxy. Instead we should consider Photoreduction and Photophosphorylation as two stand-alone processes, and that the capture of light energy to produce carbohydrates is a highly specialized phenomenon; which, from an evolutionary point of view is not really (at least not originally) part of “photosynthesis” (i.e. carbohydrate anabolism).
Even Flowering Plants not only can, but in fact most of the time do, decouple ATP/NADPH production from Carbon fixation. Indeed, much of the ATP & NADPH generated by Photosystems II & I respectively are in fact redirected to immediate energy needs, even in flowering plants.
Meanwhile, I heartily agree with Larry Moran’s thesis that it is important (nay, let’s say instead imperative) to teach students that there’s more to life than just flowering plants and humans?
Larry Moran (in very unsubtle and less than gentle terms) “suggests” such strategies should apply to teaching of all biochemistry; i.e. from simple pathways to more complex pathways.
A recent “must-read” article inspired me to respond to Larry Moran’s challenge,
… and I have cobbled together a worksheet, where I attempt to prove that photosynthesis is
1 – misunderstood (tis not really about Glucose and it’s not even about the Calvin Cycle) at least from a Biochemist’s evolutionary POV. Ecologists have justification to differ.
2 – NOT “irreducibly complex” but rather a hodge-podge cobbling by evolution over a long period of time. (cf https://embryo.asu.edu/pages/evolution-and-tinkering-1977-francois-jacob)
Larry Moran’s fingerprints are all over this work of mine, for which I really cannot claim any originality on my part.
I would be grateful for any constructive input and suggestions for improvement. Remember, the intended target audience remains high school students.
Thanks in advance and best regards,
Here it is: